In controlling active and semi-active automotive suspension systems, a position sensor is typically required to provide the controller with information regarding the position of the wheel with respect to the car body, which usually has a displacement range of several inches. The velocity of the relative displacement between the car body and the wheel is also typically required by the suspension controller, but can be obtained by differentiation of the position signal, or, preferably, by using an estimator.
Currently available position sensors include (a) LVDT's, which are an expensive option for mass production applications, (b) resistive potentiometers, which are subject to wear because of their sliding contact surfaces and (c) optical sensors, which are subject to contamination, are temperature limited and are relatively expensive. Magnetoresistive technology may be used to sense linear position but typically its application is avoided due to the requirement of temperature compensation.